The present invention relates to bifunctional cross-linking compounds; in particular, to cyclic disulfonic ester cross-linking compounds.
Alkylating agents are a major class of cancer chemotherapeutic compounds. Most clinically used alkylating agents are bifunctional compounds having two chemically reactive centers capable of reacting with and cross-linking biomolecules, such as the opposite strands of duplex DNA. Use of these agents to alkylate biomolecules leads to a variety of defects in intracellular metabolism, particularly defects in nucleic acid replication and/or transcription, which tend to be more lethal in rapidly growing cancer cells than in normal somatic cells.
Busulfan (Myleran, Burroughs Wellcome) is a bifunctional alkylating agent which is commonly used in the treatment of leukemias, Guide to Therapeutic Oncology, Bergevin, P.R., et al., eds., Williams and Wilkins, Baltimore/London (1979), p. 110. This compound is a linear methanesulfonic ester of 1,4-butanediol which functions by forming a butane cross-link between a pair of nucleophiles, such as the 7-position guanine nitrogens in opposite strands of duplex DNA. Initial nucleophilic attack at one of the butane end-carbons in the compound releases a negatively charged methanesulfonic acid group, leaving an uncharged methanesulfonic ester of 1-butanol attached to the nucleophile. A second nucleophilic attack on the opposite butane end-carbon results in cross-linking through the butane moiety, and release of a second negatively charged methanesulfonic acid group. Busulfan is more effective therapeutically than other linear disulfonic esters having cross-linking alkane moieties which are either shorter or longer than butane.
The present invention includes cyclic disulfonic esters having the general structural formula: ##STR1## where m.dbd.0 or 1, n.dbd.1-5, and R.dbd.H, CH.sub.3, CH.sub.3 CH.sub.2 or Cl. The compounds of the invention are useful as bifunctional agents for cross-linking a variety of nucleophile-containing biomolecules, such as proteins and nucleic acids. The cyclic disulfonic ester in which m.dbd.0, n.dbd.2 and R.dbd.H is effective in the treatment of a variety of mice cancers, including lymphocytic leukemia, lymphoid leukemia, melanocarcinoma, human breast xenograft and ovarian carcinoma. Cyclic disulfonic esters in which m.dbd.0, n.dbd.3 or 4 and R.dbd.H have also been shown to have anti-leukemic activity.
Unlike Busulfan-type linear disulfonic esters where the butanediol (n=4) diester is most therapeutically effective, among cyclic compounds of the present invention, the disulfonic ester of ethanediol (n=2) appears to be the most active in treating leukemic animals. The cyclic esters of the present invention are also shown herein to be effective in treating a variety of cancer types other than leukemias, particularly melanocarcinomas, breast xenografts and ovarian carcinomas.
Also unlike uncharged linear alkane disulfonates such as Busulfan, initial nucleophilic attack on a cyclic diester compound of the invention, in opening the diester ring, results in a linear sulfonate having a charged sulfonic acid end-group which remains attached to the compound. The charged end group has the capacity to affect both the solubility of the compound and its configuration in relation to the alkylated biomolecule, in the reaction period between the two nucleophilic crosslinking reaction events.
The invention further includes methods for synthesizing cyclic disulfonic ester compounds of the type described. In one method, useful particularly for synthesizing the n=1 cyclic disulfonic ester of the above structure, an alkanedisulfonyl chloride is allowed to react with a silver salt to form the corresponding silver disulfonate, which is then allowed to react with a dihaloalkane, such as dibromoethane or diiodomethane. In a second method, useful in the preparation of n=2-5 compounds, an alkanedisulfonyl chloride is allowed to react directly with an alkanediol in the presence of an alphatic or aromatic tertiary amine, such as triethylamine or collidine. The tertiary amine is added dropwise to the other reactants at a low temperature to avoid alkylation of the amine by the product ester.
A general object of the invention is to provide a new class of cross-linking compounds which are therapeutically effective in the treatment of several types of cancers.
Another object of the invention is to provide a disulfonic ester bifunctional cross-linking agent capable of reacting with a first nucleophile to produce a nucleophile-reactive agent having a sulfonic acid end group.
Yet another object of the invention is to provide a class of cyclic bifunctional alkylating compounds which are readily synthesized in yields suitable for drug testing and manufacture.
These and other objects and features of the present invention will become more fully apparent from the following detailed description of the invention and accompanying examples.